RULERS OF THE ANCIENT SEAS 69 



beds, specimeiis may he seen in almost any collection. In 

 the United States National Mvseum, the jaws of a tivelve- 

 foot blue shark are shozvn for comparison. The largest 

 tooth in that collection is 5f inches high and 5 inches 

 across the base. It takes five teeth of the blue shark to 

 fll the same number of inches. 



The Mosasaurs are descrihcd in detail by Professor S. 

 W. Williston, in Vol. IV. of the ^^ University Geological 

 Survey of Kansas.'''' There is a technical — and, conse- 

 quently, uninteresting — accotmt of Zeuglodon in Vol. 

 XXIII. of the " Proceedings of the United States Na- 

 tional Museum,'''' page 3^27. 



Fig. 12. — A Tooth of Zeuglodon, one of the " Yoke 

 Teeth," from which it derives the name. 



